Hi, I just purchased a 1990 f-250 4x4 with a 5.8 efi motor with 157, miles off of ebay. All of the pollution control was removed. It has terrible gas mileage. My question is how much would it cost to re install the pollution control? It cost me $20. to go 40 highway miles yesterday. The catalytic converter was also removed and replaced with a straight pipe. I live in South Carolina and need to drive to Ft. Worth Texas soon to pick up a goose neck horse trailer. Any ideas on how to improve my gas mileage would be appreciated. Also the 4 wheel drive works but keeps popping out of gear.

 

It is a 4x4 speed density 351W. Don't expect great gas mileauge especially while towing. The pollution controls can only do so much.

My 1991 Bronco got 7 MPGS when I got it. I removed every single pullution device and did a full-tune up with new exhaust all the way around. I was knocking back 18 MPGs with a speed density 302 and E4OD pushing a fully loaded up Bronco and my foot loved the skinny pedal roaring through town.

 

Well, malfunctioning pollution controls can ruin gas mileage, or even make the truck not run at all. I ain't ever had worse mileage when one or all of the smog parts was removed *properly*... as in, for example, if you take the EGR off, you have to make absolutely certain that there is NO leak into the exhaust port. If there is, it could draw fresh air in and this would show up as a lean condition on the 02 sensors, so the EEC adds fuel to compensate for what it thinks is the actual engine running too lean. If the intake side where the valve used to mount is leaking vacuum, this lets air into the engine without first flowing it thru the mass air meter, and the same result happens... 02 sensors see a lean condition, EEC feeds more fuel, gas mileage = junk.

If you don't want to replace the smog controls, then make sure everything is dealt with where they used to connect and then start with the usual suspects that cause bad mileage. Plugs, wires, set plug gap, air/fuel filters, oil change, check timing, make sure brakes release fully and ain't dragging, make sure 4x4 is disengaging when in 2H, etc.